Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~6~3g
. BACKGROUND OF THE INVENTION
. Field of the Invention .
There is a continuing interest in the upgrading
of fuels, particularly coal, to provide fuels having a
wide variety of applications and coming within specified
standards, such as environmental standards, physical
standards~ and the like. Because of the relatively
: large supplies of coal, much attention has been focused
on the use of coal to replace oil. Bituminous and subbituminous
coal has only limited utility as obtained from mining
operation. The coal has substantial sulfur, nitrogen
and inorganics, such as calcium salts. In order to
fulfill environmental standards, it is necessary to remove
substantial amounts of the sulfur and nitrogen. Since
. calcium and other inorganics have no fuel value, they
. .~
~ 11~6639
1 ¦ act to reduce the heat content per unit weight of coal and
2 are contaminants which must be removed from a combustion
3 zone and may interfere with the proper operation of the fuel
4 combustion. In addition, in many generation operations it
~¦ is desirous to have a liquid, rather than a solid fuel.
61 In any refining of coal to upgrade the coal to an
7 ¦ acceptable fuel, it is essential that the system be economical
8 ¦and efficient and, whenever possible, provide at least a
9 ¦portion of the materials necessary for the processing. In
10 ¦ addition, it is desirable to produce products which have
11 ¦high economic value in comparison to the original coal
12 value.
13 Description of the Prior Art
14 ¦ U.S. Patent No. 3,888,896 describes a liquid phase
15 ¦methanol synthesis process. U.S. Patent Nos. 3,816,322 and
16 ¦ 3,764,547, and patents cited therein, describe a partial
17 ¦oxidizer gasifier.
18 1
19 ¦ SU~ARY OF THE INVENTION
20 ¦ A process is provided for the economic and efficient
21 ¦upgrading of coal to a clean, light distillate fuel, a heavy
22 ¦fuel and methanol. Coal is solvent refined under severe
23 ¦conditions, preferably in a hydrogen environment, to provide
24 la substantially liquid product, which is divided in a separa-
25 ¦tion zone to a light distillate product, recycle solvent, a
26 ¦heavy fuel, and a vacuum residue slurry. The vacuum residue
27 ¦slurry provides an efficient feed for a partial oxidation
28 ¦gasifier which produces synthesis gas as-a feed for me-thanol
29 ¦production and to supply hydrogen to the above liquefier.
31 1
32 2
f ~1~6639 -
1 ¦ Hydrocarbon contaminants in the synthesis gas feed are
2 1 returned to the gasifier or otherwise processed for conversion
3 ¦ to additional synthesis gas. The heavy fuel may be used for
4 ¦ in-plant fuel requirements. Alternately, the hydrocarbon
¦ gases may be used for in-plant fuel and the heavy fuel
6 ¦ gasified with the vacuum residue.
7 1
8 BRIEF DESCRIPTION OF THE DRA~ G
9 Fig. l is a diagrammatic view of a process accord-
ing to the subject invention.
11
12 DESCRIPTION OF THE SPECIFIC EMsoDIMENTs
13 The process of the subject invèntion is concerned
14 with the efficient and economical production of light distillate
and methanol or methane. Coal, particularly bituminous or
16 subbituminous coal, and preferably the latter, are employed
I7 as the raw material.
18 In carrying out the process, a hydroliquefier is
19 employed, whereby coal is contacted with hydrogen and recycle
solven-t under severe conditions to produce high yields of
21 light distillate. The gaseous fraction is taken overhead,
22 and hydrogen recycled to the hydroliquefier. The liquid
23 fraction is transferred to a separation zone and divided
24 into a light distillate fraction, a heavy distillate fraction~
and a vacuum residue slurry. The light distillate fraction
26 is a clean fuel. The heavy dis-tillate fraction may be
27 employed internally as a heat source, may be fed to the
28 gasifier along with the vacuum bottoms, may be further
29 hydrocracked into ligh-t distillates, or stored and used for
32 3
1~ 39 ,j
1 other purposes. The residue serves as a feed stock for a
2 partial oxidizer gasifier which provides the synthesis gas
3 feed stock for methanol production. Any hydrocarbon impurities
4 from the methanol may be separated and returned to the
gasifier, used as fuel gas, or steam-reformed to make addi-
6 tional synthesis gas.
The first stage of the process is the hydroliquefier.
8 The hydroliquefier employs finely comminuted coal and hydrogen
9 donor solvent as a feedstock. Various processes for liquefy-
ing coal may be found in a wide varie-ty of patents. See for
11 example U.S. Patent Nos. 3,536,608 and 3,700,584.
12 In the subject invention, various bituminous coals
13 may be employed, but subbituminous coal is preferred, because
14 it provides a high yield of light distillate, which is low
in sulfur and nitrogen. The comminuted coal will generaliy
16 be less than about one-quarter inch in diameter, more
17 usually less than one-eighth inch, and generally from about
18 20 to 200 Tyler mesh, more usually about 40 to l00 Tyler
19 mesh. The size of the coal particles is not critical to
this invention, and substantial variation is permitted.
21 The hydrogen donor solvent is primarily partially
22 hydrogenated aromatic hydrocarbons. Mixtures of hydrocarbons
23 are generally employed, usually boiling in the range of
2~ about 260-425C. Examples of suitable solvent components
are tetralin, decalin, biphenyl, methylnaphthalene, etc.
26 Other types of solvents which may be added to the preferred
27 solvents or may be present as part of the recycle stream
28 include phenols such as phenol and cresol. The solvent may
29 be hydrogen treated prior to introduction into the hydroliquefier
to enhance the hydrogen donor capacity.
31 The operating conditions of the hydroliquefier are
32 s~ve e so d o enh~nce the pro~uction oE light distillates.
I ' 1~663~ ', `
1 The liquefier will normally be operated at temperatures
2 between about 700F and 900F, more usually between about
3 825-900F and at pressures from about 200 to 4,000 psig.
4 Reactor space rates will generally be in the range of 5 to
500 pounds oE coal per hour per cubic foot of reactor volume,
6 more usually 5 to 40 pounds of coal per hour per cubic foot
7 of reactor volume. ~hile in some instances, catalysts may
8 be added, such as oxldes or sulfides of nickel, molybdenum,
9 cobalt, and the like, supported on a high surface area
alumina or silica alumina bar, normally the process will be
11 noncatalytic.
12 The process may be carried out in the presence or
13 absence of hydrogen. Where hydrogen is employed, the amount
14 of hydrogen will generally vary from about 5 to 50 scf per
pound of coal.
16 The weight ratio of solvent to coal will generally
17 be in the range of about 1 to 10:1, preferably 1-3:1, and
18 particularly preferred 1.5-2:1.
19 The gas which exits from the hydroliquefier will
be a mixture primarily of hydrogen sulfide, carbon dioxide,
21 water, methane, and hydrogen. By employing conventional
22 scubbing techniqu~os, the hydrogen can be purified of the
23 other gases and recycled to the hydroliquefier.
24 The substantially liquid effluent from the hydro-
liquefier will be transferred to a separation zone, normally
26 a distillation section, and preferably, one which includes a
27 vacuum distilla-tion column. The hydroliquefier effluent
28 will be divided into four fractions, light distillate,
29 recycle solvent, heavy distillate, and vacuum bottoms.
Preferably, the separation is carried out in two stages,
31
32 5
(- ~:116639 (-
¦ where the distillate is divided into two fractions the first
21 fraction boiling up to 650F and the second fraction boiling
3 ¦ between about 650F and 950F. The lower boiling fraction
4 ¦ is then further separated into recycle solvent and light
5 ¦ distillate, The quantity of vacuum bottoms will be such
6 ¦ that when gasified, as described below, will supply a sub-
7 ¦ stantial excess of gas over that which is required for the
8 manufacture of make up hydrogen for the liquefier.
9 Based on the coal (dry ash free basis~, the yield
of light distillates will be in the range of about 15 to 45,
11 usually in the range of about 17 to 40 weight percent, and
12 the stream of vacuum bottoms will be in the range of about
13 40 to 80, usually in the range of about 44 to 75 weight
14 percent.
Without any further processing, the residue from
16 the separation zone is employed as a feedstock for a partial
17 oxidizer gasifier. This type of gasifier which produces
18 synthesis gas has been described extensively in the patent
19 literature. ~arious special techniques may be employed as
described in U.S. Patent Nos. 3,528,930, 3,816,332 and
21 patents cited therein. Therefore, only a brief description
22 of the process will be provided.
23 The residue, containing ash, is fed to the partial
24 oxidizer and reacted with oxygen and steam in a closed
reaction zone at an autogeneous temperature within a range
26 of about 1,800F to 3,000F, usually about 2,20QF to 2,800F.
2~ The residue and steam are generally preheated to about
28 500F, usually at least 600F. The reactor zone pressure is
29 generally about 600 to 1,000 psig, although a pressure of
3 ~ u to 3,00 psiy s pos-ible.
~1 iL116~39 (
I
1 ¦ The products from the gasifier are carbon mono~ide
21 and hydrogen, containing small amounts of carbon dioxide,
3 ¦ methane and entrained carbon. The entrained carbon may be
4 ¦ removed by conventional methods and the gas stream transferred
5 ¦ to a methanol synthesizer.
6 ¦ The hydrogen-to-carbon monoxide ratio of the above
7 ¦ gas will be shifted to increase the proportion of hydrogen.
8 The means for doing this are conventional and will be apparent
9 to one skilled in process engineering design. The acid
gases will be removed.
11 In the shift process, the synthesis gas is
12 contacted with water under conditions where carbon monoxide
~3 reacts with the water to produce hydrogen and carbon dioxide.
14 The hydrogen rich stream is then split, a portion employed
for make-up hydrogen for the liquefier and the remaining
16 portion combined with the gasifier stream to provide at
17 least the stoichiometric requirements for methanol or methane
~8 production, 2 and 3 molar proportion respectively.
19 ~hile various processes for the synthesis of
methanol may be employed, the preferred process is found in
21 U.S. Patent No. 3,888,896, which is illustrative of me~thanol
22 production from synthesis gas. The specific process carries
23 out the methanol synthesis in 2 liquid medium. Br1efly,
24 polyalkylbenzenes are used as a liquid medium and boil from
about 100C to 250C, although other liquids may also be
26 included. The reaction temperature employed ranges rom
2~ about 200F to 950F, usually from about 400F to 750F,
28 with pressures ~rom about 200 to lO,000 psia, usually from
29 about 500 to 3,500 psia. ~lormally, hydrogcn will be in excess
31 .
32 7
,' ~1
~. ~f
1116639
1 of the stoichiometric requirement, usually not more than 5,
2 more usually not more than 4 times stoichiometric. The flow
3 ¦ rate of reactants will generally be from about O.l to lO
4 1 pounds of feed per pound of catalyst per hour more usually
~ ¦ about 0.5 to 5 pounds of feed per pound of catalyst per
6 hour.
7 Any conventional methanol forming catalyst may be
8 employed, for example, a copper, chromium and zinc catalyst
9 as described in U.S. Patent No. 3,326,956.
The methanol stream which exits from the methanol
11 synthesizer will generally be contaminated with low molecular
12 weight volatile hydrocarbons. These may be readily separated
13 from methanol and the hydrocarbons returned to the gasifier.
14 Alternatively, where the stoichiometry does not provide for
complete reduction of the carbon monoxide, the unconverted
1~ reactants in the exiting gas stream may be employed directly
17 for generation of elec-tric power or for fuel. Alternatively,
18 a side stream may be taken from the gasifier effluent to be
19 used for the direct generation of electric power. In addi-
tion, the hydrocarbon purge from the methanol unit may be
21 steam reformed to make synthesis gas, which may be then
22 cycled to the methanol synthesis unit, rather than recycling
23 the hydrocarbon purge to the gasifier unit.
24 The methanol produced from excess gasification
products will generally be in the range of about 35 to 80,
26 usually 40 to 60% of the total heating value of the fuel
27 ducts.
32 ;
1 In a further variation, the methanol synthesis
2 unit may be replaced with a methane synthesis unit, so that
3 methane rather than methanol is prepared, which may then be
4 used as a fuel.
31 For further understanding of the invention, the
6 ¦ drawing will now be considered.
7 ¦ Coal (2) and recycle solvent (30) are slurried
8 ¦ together in slurry preparation section (4), the coal being
9 ¦ relatively dry and in finely comminuted form. The slurry is
10 ¦ mixed with fresh hydrogen (82) and recycle gas (23) at the
11 ¦ preheater (6). The heated products (7) flow to the liquefier
12 (8). The liquefier product (9) is separated into vapors (14)
13 and liquids (12) in the hot vapor/liquid separator (10).
14 The liquid product (12) is fed to a vacuum still (13). The
vapor products (14) are cooled and flow to a separator (20)
16 wherein the fixed gases (21) are separated from water (19)
17 and condensed hydrocarbons (26).
18 The overhead products (24) from the vacuum still
19 (13) are mixed with the condensed hydrocarbons (26) and
these are fed to an atmospheric fractionation section (28).
21 Three products are taken from the atmospheric fractionation,
22 namely: 400 x 950F recycle solvent (30), optional heavy
23 fuel (32) and net clean distillate product (34). The optional
24 heavy fuel (32) may be absent depending upon the desired
product slate. The vacuum still may be operated to leave
26 this cut in the vacuum bottoms (i.e., slurry feed (36) to
27 the gasifier (42).
28 The overhead product (21) from the separator (20)
29 is split partially into recycle gas (23~ and purge gas (22).
33l Stream (22), above, will be of such quantity to control
321 9
11 ~ ~39
1 the build up of impurities in the liquefier feed gas and
2 provide the desired partial pressure of hydrogen in the
3 liquefier. Stream (22) will contain hydrogen as well as
4 ¦hydrocarbon gases, carbon monoxide, carbon dioxide, hydrogen
5 ¦sulfide and other impurities. This stream may be admixed
6 with the gasifier output (50) or may alternately be used as
7 a source of fuel gas.
8 The vacuum bottoms product (36) and optionally
9 purge gas stream (46) are fed to partial oxidation gasifiers
(42) along with oxygen (40) and steam (44). Synthesis gas
11 consisting principally of carbon monoxide, hydrogen and acid
12 impurities (CO2, H2S, COS) is the product (50). The acid
13 gas impurities are removed in section (56). It may optionally
14 be desired to concurrently remove hydrocarbon impurities if
a physical absorption system is used for acid gas removal.
16 If this were done, part or all of stream (48) would be
17 removed as a stream from block (56) rather than from the
18 methanol synthesis purge (46). A portion of the clean gas
lQ stream (62) is shifted to form relatively pure hydrogen in
blocks (68) and (72). An aliquot of the hydrogen (82) is
21 returned to the coal liquefaction section. The remainder of
22 the gas (66) is remixed ~ith unshifted gas to form the
23 methanol synthesis gas feed (76). The split between streams
24 (62) and (64) is chosen to be such that stream (76) has a
2~ molar ratio of H2/CO being approximately equal to 2. The
26 hydrogen and CO are converted to methanol in block (78) from
27 which impurities emerge as stream (~6) and alcohol product
28 as stream (80).
29 In the above description, it should be understcod
that the key process steps have been described in their
31 concept, and that one ckilled in the engineering design of
32 10
11166;~9 ~ ~
1 process plants would recognize engineering alternatives for
2 carrying out the same process steps. In particular, it will
3 be important to the overall economics of the process to
4 efficiently recover energy (heat) from streams being cooled
and to utilize this energy to offset other process require-
6 ments. The particular choice of such items will be apparent
7 to one skilled in the art.
8 In the subject process, coal is transformed into
9 a number of high quality fuels and chemicals by means of an
economical and efficient process. Rather than using the
11 coal directly in a gasifier to produce carbon monoxide and
12 hydrogen, the process first hydroliquefies the coal under
13 severe conditions, so as to give a high yield of light
14 distillate fraction. In addition, the process provides
hydrogen for the hydroliquefaction of coal and fuel for
16 operation of the plant. The vacuum residual, which is a
I7 pumpable slurry at elevated temperature, is employed for the
18 production of synthesis gas anc utlimate production of
19 methanol. Alternatively, the process can be easily modified
to produce methane rather than methanol. A key feature of
21 the process is the coproduction of distillates and methanol
22 (or alterna-tely methane) in significant hish yields.
23 The process can easily acco~!odate an increased
24 yield of methanol if this is desired. The slurry feed to
2~ the gasifier (36) is capable of accepting additional solid
26 hydrocarbons, such as coal, while still maintaining its
27 slurry character. A substantial quantity of coal, equal to
Z8 30~ or more by weight of stream (36), may be added. This is
29 demonstrated in Example 4, below.
31
32 11
~ 6639
1 The subject process demonstrates how the hydrogen
2 and carbon values of coal can be upgraded to provide useful
3 fuels and chemicals. The various products derivable from
4 coal are integrated into a single system to produce a
~ ¦ spectrum of products, which either may be used in-ternally or
6 ¦ provide high grade fuels or raw materials for further
7 ¦ processing.
8 ¦ For purposes of illustration, the following
9 ¦ examples demonstrate the operation and benefits of the
10 1 subject invention.
11 ¦ Example l - Hydroliquefaction
12 Subbituminous coal( ) from the Wyodak Mine
13 located in Campbell County Wyoming ~Wyokak - Anderson
14 Seam) was liquefied in a continuous apparatus with
conditions and yields as follows: -
16 Coal Analysis
~7 Moisture, W% 6.4
18 Proximate, W% (dry)
19 Ash 7.0
Volatile Matter 46.5
21 Fixed Carbon 46.5
22 Ultimate, W% (dry)
23 Carbon 67.8
24 Hydrogen 5.0
Nitrogen 0.8
26 Sulfur 0.8
27 Ash 7 0
28 Oxygen (by difference)18.6
29 Heating Value (dry basis) ll,480 Btf/pound.
(l)Johanson, Edwin, So]vent Refining of Wyodak, Illinois 6, and
Black Mesa Coals, EPRI RP389 (vol. 2), Electric Power Research
31 Institute, Palo Alto, California, February 1976 (Data quoted
are Run 177-114) lZ
~ fi.~
RUN NUMBER 22 13B
21 Run Conditions
3 ¦ Coal Space Rate lb of dry coal 32 32
4 ¦ hr - Ft
5 ¦ Recycle Solvent to Coal, wt ratio 2 2
6 Temperature, F 840 835
7 Pressure, psig (pure H2 feed gas)2500 2000
8 ¦- Type of reactor Perfectly mixed flow
9 ¦ Yields, Wei~ht % of MAF(l)Coal
0 l CO2 8.25 5.84
11 I CO .61 1.77
12 I Cl x C3 9.10 5.70
13 ¦ C4 x 350F 8.23 8.28
14 ¦ 350 x 650F 11.53 8.81
15 ¦ 650 x 950F 10.01 13.08
16 ¦ + 950F Residuum Oil 36.99 34.94
17 ¦ MAF Unconverted Coal 7.38 13.19
18 ¦ H2O 10.66 10.66
19 ¦ NH3 .24 .13
20 ¦ H2S 50 47
21 ¦Total (100+ Hydrogen reacted) 103.50 102.87
22
23 )Molsture and ash free.
27
229
31
32 l3
I f-
1 ¦ Properties of Produets, W%
2 C 4 x 350 F
3 ~ Sulfur 0.09 ~
4 ~ Nitrogen 0.06 - -
~1
6 ¦ 350 x 650F
7 ¦ % Sulfur 0.40
8 ¦ % Nitrogen 0.30
9 I
10 ¦ EXAMPLE 2 - GASIFICATION OF HYDROLIQUEFACTION VACUUM
11 1 BOTTOMS SLURRY
12 Vacuum bottoms slurries from hydroliquefaction
13 processing Wyodak Coal (2) were gasified in a
14 Texaco partial oxidation gasifier. Summarized
results are as follows:
16
17 Cold Gas Efficieney - 85
18 (Gross heating value of the
19 synthesis gas as a fraetion
of gross heating value of
21 the feed)
22 SCF of Oxygen
23 Oxygen Consumption --270 SCF of 2
24 SCF of CO ~ H2
2~ EXAMPLE 3 - Integration of Liquefaction and Gasification
26 and Methanol Synthesis
27 Based on the above, Examples l and 2, the follow-
28 ing yields are projected for their combination in accord with
29 Figure l (Run 22 of Example l), wherein streams 48 and 54 are
null.
31 ( )Robin, Allen M., Hydroyen Production from Coal Liquefaction
Residue, EPRI AF-233 Final Report, ~lectric Power Research
32 ~ te
~` 1116639 ~
21 Yields, per 100 3tu net ~lower) heating value of coal.
3 C4 x 350F Distillate 12.8 Btu (LHV)
4 350 x 650F Distillate 17.3 Btu (LHV)
650 x 950F Distillate 15.5 Btu (LHV)
6 Methanol 34.6 Btu (LHV)
7 ¦ Total 80.2
8 I
9 ¦ OXYGEN REQUIRED 0.05 SCF
10 l
11 ¦ For comparison, if methanol were produced from coal
12 ¦ directly by partial oxidation, with feed in a water slurry,
13 the products would be approximately 55 to 60 Btu of methanol
14 ~LHV) per 100 Btu of feed coal (LHV), and the oxygen con-
sumption would be more than twice as high.
16 In both of the above cases, the internal plant
17 fuel requirements have not been considered. The net plant
18 fuel requirements are about equal for the two cases.
19 The advantages of the subject invention with
regard plant efficiency are thus readily apparent.
21
22 EXAMPLE 4 - ADDITION OF COAL TO VACUUM BOTTOMS
23 The following data illustrates the fluidity of
24 vacuum bo-ttoms from processing of subbituminous coal and
admixtures of that coal with the vacuum bottoms at 600F
26 Vacuum Bottoms - 0.4 poise
27 30% Coal/70% Vacuum Bottoms - 11.0 poise
28 Although the foregoing invention has been des-
29 cribed in some detail by way of illustration and example
301 for purposes of clarity of understanding, it will be obvious
311
32 15
1l f- ~11663!9 ~`
1¦ that certain changes and modifications may be practiced
21 within the scope of the invention as limited only by the
~¦ scope of t appended claims.
~2
227
29
32 1
